Hitherto, hydrazone compounds are useful as photoconductive substances for use in electrophotographic photoconductors and their application to electrophotographic photoconductors and production processes have been disclosed (see, e.g., Patent Documents 1 to 5).
Patent Document 1: JP-A-06-166667
Patent Document 2: JP-A-02-308862
Patent Document 3: JP-A-02-308861
Patent Document 4: JP-A-61-23154
Patent Document 5: JP-A-60-255854
A hydrazone compound can be generally obtained by reducing an N-nitrosoamine compound to form a hydrazine compound and subsequently, after it is taken out as a hydrochloride salt, subjecting it to a condensation reaction with a carbonyl compound. In the case that it is intended to produce a hydrazone of industrially high quality in a high yield, it is required to obtain an easily oxidizable and unstable hydrazine compound in high quality and in a high yield at the completion of reaction. Furthermore, most of N-nitrosoamine compounds and hydrazine compounds are known to have toxicity (mutagenicity). Therefore, from the viewpoint of securing safety of workers, an exposure-preventing measure for workers against N-nitrosoamine compounds and hydrazine compounds is highly required.
As mentioned above, many of hydrazine compounds are very instable and easily oxidized and, in the case that hydrazine compounds are once taken out after N-nitrosoamine compounds are reduced, cases where it cannot be converted into hydrazone compounds or a remarkable decrease in yield may occur, so that this is mostly not suitable as an industrial production process for producing hydrazone compounds. There have been disclosed contrivances for avoiding these problems. For example, there has been proposed a process for producing a hydrazone compound, which comprises adding an sodium nitrite solution to a solution of 1 part by weight of N-phenyl-N-α or β-naphthylamine dissolved in 3 to 30 parts by weight of an organic acid to form an N-nitroso compound, subsequently reducing a solution containing the corresponding N-nitrosoamine, and condensing a reaction solution containing thus formed N-phenyl-N-α or β-naphthylhydrazine with a corresponding carbonyl compound (see, e.g., Patent Documents 6 and 7). In this process, since the N-nitrosoamine compound is reduced by a powder of a metal such as zinc and acetic acid, a filtration step of a residue of the reducing agent is indispensable in the post-treatment of the reaction. Due to the filtration step, oxidative decomposition of the hydrazine compound is still promoted and, as a result, a decrease in yield (about 60%) of the hydrazone compound as a final target compound and a decrease in quality thereof occur. Moreover, at the time of the filtering operation and the handling of the filtration residue, the exposure of workers to the hydrazine compound is unavoidable and thus, also from the viewpoint of securing safety of the workers, the process is not suitable as an industrial process for producing a hydrazone compound.
Hitherto, a hydrazine compound is obtained by reducing an N-nitrosoamine compound with zinc powder-acetic acid, sodium-ethanol, sodium-liquid ammonia, lithium aluminum hydride, or the like, separating the hydrazine compound from the reaction mixture, and further purifying it by salting-out, rectification distillation, chromatography, recrystallization, or the like. However, all these reducing agents are accompanied by danger in handling and also treatments of the residue of the reducing agents and the waste liquid after the reaction is vexatious and complex. Also, since the N—N bond is apt to be cleaved and the yield of the hydrazine compound is not sufficient, the process is industrially not satisfactory. A contrivance for avoiding the problems has been disclosed (see, e.g., Patent Document 8). The process disclosed in Patent Document 8 is a process for reducing an N-nitrosoamine compound with thiourea dioxide and an alkali in an aqueous medium. However, since the hydrazine compound is taken out, the exposure of workers to the hydrazine compound is unavoidable and also the cleavage of the N—N-bond can be not completely suppressed, so that the process is not suitable as an industrial process for producing a hydrazone compound.
Patent Document 6: JP-A-59-39860
Patent Document 7: JP-A-58-65261
Patent Document 8: JP-A-1-224333